The CAN bus is a differential bus system having high signal symmetrization demands. The better the signal symmetrization, the lower will be the interference emission and the interferences at a subscriber station such as a car radio, for example. Signals CAN_H and CAN_L, which are in phase opposition, must be controlled in such a way that their mean value deviates preferably little from mean voltage VCC5/2=2.5V.
Signal symmetrization is presently achieved by balancing the resistances of the switches to ground GND and to potential VCC5, in such a way that in the dominant state of the bus, in which the differential voltage of the signals CAN_H-CAN_L has a value of approximately 2V, the mean voltage is 2.5V. The switch resistances are balanced out by skillful dimensioning, for example, by adjustment or by control circuits, such as those described in German Patent Application No. DE 10250576A1.
However, it is problematic that the symmetrization during the switching operation is inadequate since one switch to VCC5 (pull-up switch) and one switch to GND (pull-down switch, GND=ground) have different characteristics. The total voltage at the switching point has voltage peaks (spikes), which result in a poor emission behavior in the high-frequency range, a range above 1 MHz. In the related art, these interfering voltage peaks are suppressed by a common mode choke. However, such a common mode choke is an additional component, causing additional costs and requiring additional space, which is usually available only to a very limited extent.